The present invention relates to a device for detecting and controlling a desired grinding condition of a piezoelectric element. More particularly, the device is designed to detect a desired natural frequency, employing two filters which provide equivalent damping amount at a desired natural frequency of a piezo-electric element.
In conventional grinding of a crystal piece for obtaining a specified natural frequency, crystal pieces are first mounted on a grinding apparatus to undergo rough grinding for a period that has been measured in advance, and each crystal piece is then taken out to make measurement of the individual natural frequency. When the frequency proves not to have reached a specified natural frequency, re-grinding is carried out. Therefore, it requires longer time for adjustment, and requires much labor since each crystal piece has to be taken out every time measurement of the frequency is made.